Ozone, which protects Earth's life from harmful
radiation,
is being manufactured one-half billion miles away, on
Jupiter's largest satellite,
Ganymede. Hubble found ozone's spectral
fingerprint during observations of Ganymede made by Keith Noll
and colleagues at the Space Telescope Science Institute, Baltimore,
Maryland. The amount of ozone detected on Ganymede is small by
Earthly standards. The total is only a tiny fraction (between
1-10 percent) of the amount of ozone destroyed each winter in
Antarctica's ozone hole (a location on Earth where ozone levels
seasonally drop to extremely low
levels).

Unlike ozone production in Earth's atmosphere, Ganymede's ozone is
produced by charged particles trapped in Jupiter's powerful magnetic
field (much like the Earth's Van Allen radiation belts). Jupiter's
9-hour, 59-minute rotation sweeps these particles along at tremendous
speed, where they overtake the slower moving Ganymede and rain
down onto the surface. The charged particles penetrate the ice surface
where they disrupt water molecules, but the exact steps leading to ozone
production are not yet fully understood, according to Noll.

Though no atmosphere has yet been detected on Ganymede, "the
evidence for all this oxygen chemistry going on in the surface ice is
a strong hint that Ganymede also will turn out to have a tenuous oxygen
atmosphere," said Noll. Earlier this year, Hubble detected a thin
oxygen atmosphere on the Jovian moon Europa.

Ganymede, Jupiter's largest moon (5,262 kilometers or 3,280 miles in
diameter; 1.5 times the size of the Earth's Moon),
is thought to be composed of rock and ice beneath which lies a water/ice
mantle and rocky core.

The Space Telescope Science Institute is operated by the Association of
Universities for Research in Astronomy, Inc. (AURA) for NASA, under
contract with the Goddard Space Flight Center, Greenbelt, Maryland.
The Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency (ESA).